Typical uncertainties in the zero points of the P/L relations of RR Lyrae stars are thought to be of order 0.05 mag [1]} and other methods like CMD fitting have
similar uncertainties. In addition, the reddening of many clusters presents an additional challenge for the determination of accurate distances since it can be variable even across small,
arcminute size fields [2]}, [3]}. Furthermore there is evidence for non-standard reddening laws in the directions of several globular clusters like for example M4 [4]}, [5]}.
